1. Field of the Invention
This invention relates to a medium for gel electrophoresis (hereinafter referred to as "gel medium") used to determine base sequence of DNA, DNA fragment and DNA derivative, and in particular provides a composition of gel medium to improve workability of the medium.
2. Description of Prior Arts
In the method for determination of the base sequence of DNA, RNA, their fragments, and their derivatives according to the post-label method, the operation of slab electrophoresis using a polyacrylamide gel membrane becomes essential. The polyacrylamide membrane used for this purpose is obtainable, for instance, by a crosslinking polymerization between approx. 95 parts by weight of a monomer such as acrylamide and approx. 5 parts by weight of a bifunctional crosslinking agent such as N,N'-methylenebisacrylamide in an aqueous solution containing a mixture of the monomer and the crosslinking agent and a polymerization initiator (hereinafter referred to as "gel forming solution").
Recently, as the study concerning the gene has progressed, a rapid operation for determination of DNA base sequence is required. The electrophoresis using the polyacrylamide as the electrophoresis medium layer becomes almost essential for performing the determination of DNA base sequence, because the polyacrylamide medium gives prominently high resolution.
However, the conventional polyacrylamide gel membrane has a serious disadvantage that the membrane is brittle and easily breakable. Therefore, a polyacrylamide gel membrane for determination of DNA base sequence is generally prepared by a process in which a gel forming solution is poured into a cell formed with two glass plates (having a certain space with thickness of 0.3 to 1 mm) to prepare a gel membrane in the cell. To the gel membrane, sample inlets must be provided so that the membrane can receive DNA samples (Maxam-Gilbert decomposed .sup.32 P-labeled DNA or etc.). Accordingly, a sample slot former is generally inserted into the cell after the gel forming solution is poured therein but before gelation takes place, so that the sample slots can be provided to the gel membrane. It is difficult to cut off the edge from a prepared membrane with a razor or the like to provide the sample inlets, because the gel membrane is very brittle and easily breakable, as descirbed above. For this reason, the above mentioned process involving the provision of sample slots by insertion of the sample slot former in advance of the gelation is utilized. This complicated process is a serious obstacle in producing the polyacrylamide gel membrane on a mass scale.
The polyacrylamide gel membrane prepared as above is then kept vertically together with the glass plates, and the sample slot former is removed. A certain amount of a sample (Maxam-Gilbert decomposed .sup.32 P-labeled DNA or etc.) is poured into the sample slots, and the sample is electrophoresed. The electrophoresis is continued for a certain period of time, one glass plate is removed carefully, and the autoradiographic process is performed on the gel membrane. Thereafter, the determination of DNA base sequence is carried out. Even in this process, the gel membrane sometimes breaks when the glass plate is removed, because the conventional gel membrane is very brittle. Thus, the brittleness of the conventional membrane is a very serious problem.